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During the membrane cutting step, robotic inspection ensures that each membrane is cut precisely and accurately, for reliable performance. This quality control system analyzes and displays parameters for 16 membrane discs at a time.

Good manufacturing practice and ISO® 9001 Quality Standard: Millex® filters are manufactured in a facility whose Quality Management System is approved by an accredited registering body to the ISO® 9001 Quality Systems Standard

What other aspects of quality materials contribute to the high performance of Millex® filters?

Low-extractable housing

Very low levels of extractables from housing materials selected for Millex® filters is due to the broad, high chemical compatibility of both HDPE and PP materials.

Click images to enlarge.

Evaluation of the extractables profile of the housing materials of Millex® filters.

The experimental procedure for performing extractable analysis was as follows:

Syringe filter devices without the membrane were prepared and different solvents were filtered through it.

Following filtration, 1 mL fractions were collected and analyzed by reversed phase chromatography using a C18 column and a water/ acetonitrile gradient from 0-100% acetonitrile.

No peak was observed in the chromatogram indicating absence of any extractables.

The peak observed at about 2 min. is a solvent front / void volume peak whereas peak observed at 17 min. happens due to end of gradient switch to 0% acetonitrile from 100% acetonitrile.

Typically sample is not dissolved in exactly the same solvent as the mobile phase, and the solvent component from the injected sample elutes out first as it is not retained at all by the column. Since the solvent might have a slightly different absorbance at the detection wavelength (214nm in our example) a small peak may appear at the solvent front.

Similarly, when the gradient switches from 100% organic solvent to 100% aqueous sample, there is a sudden change in absorbance, which shows up as a peak at the end of the chromatogram. In normal chromatography the goal is to always stay away from the solvent front (because otherwise there is no retention and separation) and away from the end of gradient (because there is too much retention). The goal is to elute the analyte in the middle portion of the chromatogram.

HPLC-Certified Filters: Not Necessarily Clean

Note that all HPLC-certified filters are not equally clean. HPLC-certified filters from different vendors are all labeled as having “low levels of extractables.” Because methods of extractables testing differ between different vendors, a result that appears low under certain testing conditions can be higher under other HPLC conditions.

As can be clearly seen from the chromatograms below, all these HPLC-certified syringe filters show very different extractables profiles. The hydrophilic PTFE syringe filters show the least amount of extractables whereas the nylon syringe filters show very strong peaks between 4 – 6 min. On the other hand, the polypropylene membrane shows a broad peak between 4 – 7 min. This elution time range can be the critical range during which analytes of interest elute, and the presence of these extractables makes quantitation and identification much more difficult.

In the extractables analysis experiment shown, 70% acetonitrile in water was filtered through various syringe filters and the first mL of the filtrate was analyzed by reversed phase HPLC with UV detector set to 214 nm. HPLC was carried out using a C18 column and 0 – 100% acetonitrile gradient to ensure elution of all the impurities / extractables from the column. (Click image to enlarge.)